1. Field of the Invention
The present invention relates to an oscillation apparatus.
2. Description of the Related Art
Hitherto, various types of oscillation apparatuses have been used in extensive fields.
As technology of stabilizing a frequency of an oscillation signal in the conventional oscillation apparatus, there is adopted, for example, a PLL scheme in which an external periodic signal as a reference signal is inputted, a deviation from the external periodic signal is detected, and there is provided such a regulation that when a deviation occurs owing to a disturbance and the like, such a deviation disappears as soon as possible.
By the way, now let us consider, for example, the rhythm of the human life. It will happen that when a person wakes up earlier than usual in a certain morning owing to some causes, the person will begin to feel sleepy earlier than usual on the day, and the earlier sleeping may involve the earlier waking up in the morning. In this manner, an influence of the disturbance such that a person wakes up earlier than usual on a certain morning will not be restored immediately, but will be recovered little by little to ones former rhythm over several days.
Also it happens that for example, when a person plays a musical instrument along to metronome sounds and is aware of the fact that he plays without harmonizing with the metronome sounds, it is preferable that the musical performance is regulated little by little slowly so as to harmonize with the metronome sounds in such a manner that an audience does not feel out of place.
Further, also it happens that for example, when the metronome sounds are too fast to meet his musical performance pace, the metronome sounds are neglected every other sound to conduct a performance with a half tempo, or oppositely, when the metronome sounds are too slow to meet his musical performance pace, the performance is conducted at twice tempo as compared with the metronome sounds.
Recently, there has been developed a system in which an artificial creature is built in a computer and behaves in the computer just as if the artificial creature has one's own intention and emotion. With regard to such a system, there is made an effort such that the rhythm of the artificial creature and a tempo of the musical performance approaches that of the actual creature, but not the robot-like one. In order to produce the fundamental living rhythm of the artificial creature or to produce a tempo of the musical performance in the event that the musical performance is to be conducted without remarkably changing a tempo of the musical performance, a kind of oscillation apparatus is used. In such a use, it is preferable to adopt an oscillation apparatus which is operative in such a manner that an influence of the disturbance is not restored immediately, but is recovered little by little over a predetermined time, as mentioned above, and in addition, in another situation, the oscillation apparatus oscillates in a period not identical to a period of the external signal, but having a certain relation with respect to the period of the external signal, such as half or twice of the period of the external signal.
By the way, when it is intended that such an oscillation apparatus is implemented through the prior art, there may be considered, for example, an arrangement in which an variation in a frequency of an oscillation signal due to the disturbance is detected and a frequency of an external periodic signal is varied, and the varied frequency of the external periodic signal is recovered little by little over a predetermined time so that the oscillation frequency is recovered taking the predetermined time. However, according to these systems, the oscillator itself intends to oscillate as faithfully as possible, and it is obliged to control the frequency of the external periodic signal. This involves such a problem that the structure is complicated.
In order to solve such a problem, it is preferable to implement an oscillation apparatus which is operative in such a manner that an oscillation frequency is recovered little by little on a self-control basis in the interior, but not to access from the exterior, and in addition, in another situation, the oscillation apparatus oscillates in a period not identical to a period of the external signal, but having a certain relation with respect to the period of the external signal.
An oscillation apparatus, which satisfies such a requirement, has been proposed by the inventors of the present application (cf. Japanese Patent Application No. 7-211899) which corresponds to U.S. Pat. No. 5,815,045. According to the proposed oscillation apparatus, however, there is a need to feed from the exterior an input signal, which periodically varies in value, for example, having a sine wave, and it is impossible to feed from the exterior a pulse sequence consisting of sequentially continued pulses to generate a signal synchronized with the pulse sequence.
In view of the recent tendency of a digitalization of signal processings, it is preferable to provide an oscillation apparatus in which a pulse sequence is fed from the exterior so that a signal synchronized with the pulse sequence can be generated.